Process for drying slime, particularly foul slime, and plant for executing the said process



Feb. 18, 1958 a w. LUDlN EI'AL 2,823,742

PROCESS FOR DRYING sums, PARTICULARLY FOUL SLIME, AND PLANT 'FOR EXECUTING THE SAID PROCESS Filed Aug. 13, 1951 3 Sheets-Sheet 1 Fig. 1

Feb. 18, 1958 w. LUDIN ETAL 2,823,742

PROCESS FOR DRYING SLIME, PARTICULARLY FOUL; SLIME, AND PLANT FOR EXECUTING THE SAID PROCESS Filed Aug. 13. 1951 s Sheets-Sheet 2 Fig.2

I 30 Fly. 3 24 23 Feb. 18, 1958 w. LUDIN ETAL 2,823,742

PROCESS FOR DRYING SLIME, PARTICULARLY FOUL SLIME, AND PLANT FOR EXECUTING THE SAID PROCESS Filed Aug 13, 1951 3 Shasta-Sheet 3 Fl .4- J;

7 I Y 5 1 I u PROCESS FOR DRYING SLIME, PARTICULARLY FOUL SLIME, AND PLANT FOR EXECUTING THE SAID PROCESS Werner Ludin and Fritz Bion, Zurich, Switzerland, as-

signors to L. von Roll A. G., Zurich, Switzerland, a company of Switzerland Application August 13, 1951, Serial No. 241,632

Claims priority, application Switzerland August 14, 1950 Claims. (Cl. 159-24) The drying of plastic materials such as slirnes, particularly foul slime, causes considerable technical difiiculties, since materials of this type tend to form clods and to stick to the heating walls, stirring devices and the like. The clod formation can prevent the equal and uniform drying of the material and always causes a retardation of the drying process.

To avoid these difiiculties it has been suggested that the drying be effected in several stages and that for each stage a special device should be used. Thus, it was suggested that a drum dryer be used for the first stage where the material is still in a liquid state and that in the second stage a plate or band dryer be used which will then be more suitable for plastic materials. How ever, even with this combined drying system, which employs several dryers, clod formation could not be prevented and fast and uniform drying of the material was vals, whereby an increase in temperature is caused in the materials to be dried. In certain materials the subsequent vacuum period can effect the dissolution of clods due to the momentary vapour development inside the material.

H An advance in drying technique was recorded due to fact-,'that the material is given shape after a certain initial drying, whereupon the thus obtained shaped pieces will be further dried. After short drying, the pieces retain their shape and can then be further dried in other dryers until they are completely dry. With this apparatus the difficulty of the sticking of the material to the drying devices is eliminated. However, this apparatus is also very expensive as it consists of several separately arranged drying devices which are connected with each other by conveyor belts.

, The present invention is directed to a process anda drying device for drying slime, particularly foul slime, in which all the equipment necessary for the drying process is grouped together and in which particular care is taken for best utilization of the heat supplied. Therefore, the drying plant "is much simpler in construction and considerably less expensive to build than other known plants. Furthermore, the space required is for such drying plant and equipment much smaller which is also an important advantage.

The process for drying slime, particularly foul slime, in which the slime to be dried is fed by means of a pump for viscid materials from a reservoir first to a pre-heater and then to several heated devices is characterized in that the vapours originating in the evaporator of the plant are directly led to a compressor and the vapours originating in the dryer of the plant are led to the compressor via a washer, the vapors being then pressed into the evaporator and the plates contained in the dryer for heating the same, whereby at least the condensate originatingin the evaporator isfed. to the Patented Feb..18, 1958 stuffing boxes of the compressor for cooling and lubricating the same, and that in the evaporator as well as in the dryer the slime is moved by rotating brushes and scrapers and that at least after that drying stage after which the slime tends to form clods, the slime is divided into parts or strips e. g. rods of small cross-section for further drying.

The slime drying plant for executing the process consists of a reservoir for the slime, a pre-heater, an evaporator and a dryer consisting of several heated devices, a pump for viscid material for feeding the slime from the reservoir to the pre-heater and means for heating the pre-heater, the evaporator and dryer and is characterized in that at least after that heated device in which the drying process of the slime has progressed so far that the slime coagulates or has the tendency to stick and form clods, means are provided for dividing the slime in preshaped parts, such as rods of small cross-section.

In the accompanying drawings, an example of a slime drying plane in accordance with the present invention is shown. In the drawings:

Fig. l is a diagrammatic view of the arrangement of the components of the drying plant,

Fig. 2 is an elevational view partly in section of a drying plant according to the invention,

Fig. 3 is a plan view of Fig. 2,

Fig. 4 is a partial section of parts of the drying equipment proper employed in said drying plant.

Fig. l is a diagrammatic view of the arrangement of the drying plant in which 1 designates the reservoir for furnishing the foul slime. From this reservoir the foul slime passes through the pump 2 for viscid material to the pro-heater 3. The pre-heater 3 is followed by the evaporator 4 from which slime is fed to the plate dryer 6 through duct 5. This plate dryer is only shown diagrammatically, as the drive members of the plate dryer are not shown. All the plates 7 of the dryer are heated in any suitable manner. The slime passes from one plate to the next one and at last, when it is dry, leaves the dryer through the lock 8 in the direction of the arrow. Hot vapours are formed in the evaporator 4 which are led from the uppermost region thereof to a compressor 10 through a duct 9 indicated by dot-anddash lines. In the compressor the hot vapours are compressed whereby their temperature is increased. The vapours are then lead and distributed, through the ducts 11 and 12 shown by double dot-and-dash lines, to the evaporator 4 and to the plates 7. The vapours originating in the dryer 6 are fed from the uppermost region thereof to a washer 14 through a duct 13. From the washer the vapours pass through a duct 15 into the duct 9 leading to the compressor 10. The condensate leaves the washer 14 through the duct 16 and is led intoa tank 17 where it is collectedand from which it is" fed, by means of a pump 17a, to the pre-h'eater 3 and to the vapour washer 14, respectively. The condensate from the pro-heater passes through the duct 18 (dot-and-dash line) to the tank 19 and is fed to the stuffing boxes of the compressor 10 by means of a pump 20. After having served for cooling and lubricating there, the condensate leaves the system. Finally, a water ring ptunp 21 is provided for removing gases which have not condensated and, if necessary, air from the intake lock 8 of the dryer.

This short description of the arrangement of the slime drying plant shows already that maximum utilization of the available heat is eifected by the arrangement of the gas passages. Figs. 2 and 3 show the actual construction of the drying plant. The dryer which is arranged centrally is designated by 22. From the slime reservoir 23 the slime is fed, by the pump 24 for viscid materials, to the .dryer 22, i..e. to the pre-heater, as can be seen in the diagrammatic view in Fig. 1. The dried material leaves the dryer through the lock and is then fed to a reservoir for dried slime 27 by means of a bucket conveyor 26. The two-stage compressor unit for compressing the vapours removed from the evaporator through the duct '28 is designated as 29. The condensate container is designated by 30, the vacuum pump by 31.

Fig.4 shows the construction of the actual dryer. The latter consists of a casing 32, preferably of cylindrical shape, in which a motor 33 is mounted at the upper end. The motor 33 drives a central shaft 34 which rests in a bearing 35 at the lower end of the casing 32. This central shaft 34 carries a lever 39 to which brushes 38 are fastened for moving the foul slime.

in operation, the slime is introduced into the dryer through an intake duct 36 and into the annular channel 36a between the wall of casing 32 and a first wail 36b. The channel 36a is located adjacent the preheater 37 and thus defines the preheating zone.

Upon filling of annular channel 360, the slime overflows into an annular channel 360 formed by and between the wall 36b and the first annular heater body or element 36d. The heater body 36d is connected to the conduit 11 leading from the compressor, e. g. 10 (see Fig. l), by means of about tweleve circumferentially spaced pipes 36 The body or element 3611 is fixedly supported by these pipes 36 so that beneath the lower edge of said element 36d there remains a flowpassageway for the slime. The upper edge of the annular body or element 36d is located at a somewhat higher level than the upper edge of the wall 36b to ensure that the slime will always first flow directly into the annular channel Eds.

The slime is now divided and flows through the two channels 36i and 36k formed, respectively, by and between the first heater body 3611! and the second annular heater body or element 36g and by and between said second heater body 36g and the wall 3tl1 of the outflow duct or channel 41. In order to assure continuous flow of the slime through the duct 41 and to prevent any possible damming up of the slime, the upper edge of the wall 36h is disposed at a lower level than the upper edge of the annular body 36g.

The two annular heater bodies or elements 36:! and 36g and the channels 36c, 361' and 36k thus will be seen to constitute the evaporator portion or zone of the dryer. The hot vapors which emanate from the slime in the evaporator zone are exhausted from the latter through outlets 40. The preheater 37 (3 in Fig. l) and the evaporator 36c '--d-gi-k (4 in Fig. 1) together constitute preliminary heating means.

As may be seen from Fig. 4, the brushes 38, which rotate with the shaft 34, continually keep the slime within each of the annular channels, i. e., in the preheating and evaporator zones, in motion and thus prevent caking thereof on the surfaces of casing 32, insulating wall 3-612, and heater bodies or elements 36d and 36g. The slime, after passing through duct -41 reaches the plate drying means, i. e., the final heating means. A number of scrapers or brushes 43 which are also driven by the central shaft 34 traverse the plate dryers 42. In Fig. 4, a ring-shaped sieve 44 is shown at the third plate dryer through which the slime is pressed. Thereby the slime is divided into individual parts in the form of strips or rods-of small cross-section and, in this form, reaches the next plate 45. In the subsequent stages or plates 45 the rods having small cross-sections are completely dried and crumbled, additional brushes 43 being provided for the plates 45 to aid in this process. The crumbled rods then pass, through the lock 46, to the bucket conveyor by which they are moved to the container for dried material. All the plate dryers are, of course, hollow and are heated by vapors coming from the condenser 10 through ducts 12.

The sieve 44 is suitably arranged after the plate where the material to be dried has reached a state in which it tends to form clods. It is known that the material cannot be dried after it has formed clods since the surface is then too small and only a small layer of the clod dries. Due to the division in parts or strips of small cross-section the clod formation is either entirely prevented or, if clods have already formed, the disadvantage of clod formation is at least eliminated. Since not all substances tend to form clods at the same stage it is not possible to state exactly after which plate the sieve must be installed. However, the general arrangement of the dryer permits the installation of the sieve at any position. Therefore, the plant can be used not only for a certain slime but for many kinds of material in plastic state. Vapors collected in the lower part 32a of casing 32 may escape through a conduit 13a as indicated, which corresponds to conduit 13 of Fig. 1.

As shown by the embodiment of the drying plant, all the components necessary for the drying process are assembled together in one simple dryer. Apart from this, auxiliary components or devices are provided which co operate with the dryer in such manner that maximum utilization of the heat is effected. In the operation of the plant a temperature increase of 20 on compressing the hot vapours has proved suitable. It is also advantageous to operate the dryer with a light vacuum. However, these values are only examples. Depending on the properties of the material to be dried other temperature increases and other pressure conditions in the dryer may be more suitable.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In a drying plant for treating slime and like viscid mass; an upright casing having an upper part and a lower part, transverse partition means fixed in said casing and separating said upper and lower parts thereof, a motordriven rotatable shaft extending substantially centrally through said partition means and said upper and lower parts of said casing, first duct means communicating with the interior of said upper part of said casing adjacent and above said partition means and defining an intake for admitting said mass into the lowermost region of said upper part of said casing, a substantially cylindrical preheater located exteriorly of and surrounding said upper part of said casing, a first substantially cylindrical body mounted on said partition means interiorly of said upper part of said casing and disposed concentrically about said shaft, at least one second substantially cylindrical heating body located within said upper part of said casing and disposed concentrically about said shaft and between the latter and said first body, said heating body being vertically spaced from said partition means, whereby a tortuous up-and-down flow path for said mass from said first duct means and through said upper part of said casing is definedby said first and second bodies, the latter together with said preheater constituting preliminary heating means for said mass, brushing means carried by said shaft in said upper part of said casing and contacting the vertical surfaces of said second body for moving said mass past the same upon rotation of said shaft as said mass is partly dried, a plurality of vertically spaced plate drying means arranged concentrically about said shaft in said lower part of said casing below said partition means, each of said plate drying means being provided with at least one aperture extending therethrough, second duct means extending through said partition means at a location between said heating body and said shaft for discharging said partly dried mass onto the uppermost one of said plate drying means, respective scraper means carried by said shaft for rotation therewith and extending over and in contact with said plate drying means to effect movement of said partly dried mass over each plate drying means to the aperture therein, thus causing said mass to fall from each plate drying means to'the next lower plate drying means and in the direction of the bottom of said casing, sieve means covering said aperture of at least one intermediate plate drying means, whereby said partly dried mass upon passage from said intermediate plate drying means to the next lower one is divided into strip-like formations to facilitate drying thereof on those of said plate drying means beneath said sieve means as well as crumbling of said mass by said scraper means associated with said last-named plate drying means, and outlet means in said lower part of said casing for receiving said mass in substantially fully dried and crumbled state from the lowest of said plate drying means.

2. In a drying plant according to claim 1; at least one additional substantially cylindrical heating body located between said first-named heating body and said shaft and concentrically about the latter, said second duct means being located between said shaft and said additional heating body.

3. In a drying plant according to claim 2; a compressor, means communicating with said upper part of said casing and with the suction side of said compressor for conducting to said compressor vapors liberated from said mass due to operation of said preliminary heating means, whereby said vapors are compressed in said compressor and their temperature raised, and further means communicating with the pressure side of said compressor and with said heating bodies and with said plate drying means for distributing said compressed vapors to said heating bodies and to said plate drying means, respectively, to heat the same.

4. In a drying plant for treating slime and like viscid mass; an upright casing having an upper part and a lower part and a bottom for said lower part, transverse partition means fixed in said casing and separating said upper and lower parts thereof, a motor-driven rotatable shaft extending substantially centrally through said partition means and said upper and lower parts of said casing, means communicating with said upper part of said casing at a location a short distance above said partition means and defining an intake for admitting said mass into the lowermost region of said upper part of said casing, an annular preheater located exteriorly of and surrounding said upper part of said casing substantially coaxially with the latter, a first annular body mounted on said partition means interiorly of said casing and about said shaft, at least one second annular heating body located within said upper part of said casing about said shaft, said heating body being spaced from said partition means and arranged between said shaft and said first body, whereby a tortuous up-and-down flow path for said mass through said upper part of said casing is defined by said first and second bodies, brushing means carried by said shaft in said upper part of said casing and contacting said second body for moving said mass past the same upon rotation of said shaft as said mass is partly dried, said bottom being provided with an outlet opening, a plurality of vertically spaced plate drying means arranged in said lower part of said casing below said partition means and each provided with at least one aperture extending therethrough, overflow-type duct means extending through said partition means at a location between said shaft and said heating body for discharging said partly dried mass onto the uppermost one of said plate drying means, respective scraper means carried by said shaft for rotation with the latter and extending over and in contact with said plate drying means and said bottom to effect movement of said mass over each plate drying means to the aperture therein and over said bottom to said outlet opening, thus causing said mass to fall from each plate drying means to the next lower plate drying means and from the lowest one of said plate drying means onto said bottom of said casing and from said bottom through said outlet opening, and sieve means covering said aperture of at least one of said plate drying means above said lowest plate drying means, whereby said partly dried mass upon passage through said sieve means is divided into strip-like formations to facilitate drying thereof on those of said plate drying means beneath said sieve means as well as crumbling and granulating of said mass by said scraper means associated with said last-named plate drying means, whereby said mass is received on said bottom of said casing in substantially fully dried and crumbled state from said lowest of said plate drying means.

5. [n a drying plant according to claim 4; a compressor having a pressure side and a suction side, said heating body and said plate drying means being provided with hollow interiors, first means establishing communication between the uppermost region of said upper part of said casing and said suction side of said compressor, second means including vapor washer means establishing communication between the uppermost region of said lower part of said casing and said suction side of said compressor, and third means establishing communication between said pressure side of said compressor and said hollow interiors of said heating body and said plate drying means, respectively, whereby vapors liberated from said mass in said upper and lower parts of said casing are led, respectively, directly to said compressor through said first means and directly to said washer means and thence to said compressor through said second means, said vapors being compressed and their temperature raised in said compressor and thereafter being distributed through said third means to said heating body and said plate drying means for heating the same.

References Cited in the file of this patent UNITED STATES PATENTS 408,824 Cazin Aug. 13, 1889 1,391,510 Schjelderup Sept. 20, 1921 1,528,698 Robinson Mar. 3, 1925 1,863,109 Graves June 14, 1932 1,980,326 Eichengrun Nov. 13, 1934 2,439,384 Fetzer Apr. 13, 1948 FOREIGN PATENTS 533,303 France Feb. 27, 1922 51,888 Norway Dec. 19, 1932 

